The invention relates to a method of enhancing open cell formation in making extruded alkenyl aromatic polymer foams of about 30 percent or more open cell content.
Open cell alkenyl aromatic polymer foams are taught in the art as useful in a variety of end-use applications such as in insulation, roofing recovery, and absorbency. Such foams and applications for them are seen in U.S. Pat. Nos. 5,434,195 and 5,557,896 and Canadian Application 2,129,278.
A problem in making open cell alkenyl aromatic polymer foams is achieving consistent and elevated levels of open cell content while avoiding high foaming temperatures. High foaming temperatures can cause foam collapse resulting in high foam density and small cross-section.
One means employed in the art to more easily achieve elevated open cell content is to employ loadings (i.e. 3-10 weight percent based upon weight of the alkenyl aromatic polymer) of dissimilar, nonmiscible polymers in the alkenyl aromatic polymer material comprising the foam. The dissimilar, nonmiscible polymers help to open cells by forming domains in the walls of expanding cells. The domains increase the likelihood of pores developing in the walls of cells. In making open cell alkenyl aromatic polymer foams, conventional dissimilar, nonmiscible polymers employed have included polyethylenes such as low density polyethylenes, linear low density polyethylenes, and high density polyethylenes.
There are disadvantages to using the conventional dissimilar, nonmiscible polymers. First, the amounts typically required were relatively high (i.e. 3-10 weight percent). The excessive amounts have resulted in additional expense as well as negatively impacted the physical properties of the end product foam. Second, they have typically exhibited only limited effectiveness in opening cells.
Another means employed in the art to more easily achieve elevated open cell content in extruded alkenyl aromatic polymer foams is to employ elevated foaming temperatures (typically about 135.degree. C. or more). However, employing elevated foaming temperatures to produce the desired level of open cell content without foam collapse can be disadvantageous because foaming temperature range may be narrow. If there is foam collapse, foam density may be increased, foam cross-section may be reduced, and skin quality may be negatively impacted.
It would be desirable to have a method for making an open cell alkenyl aromatic polymer foam wherein the desired level of open cell content is more easily and consistently maintained without the need for high loadings of conventional dissimilar polymers. It would also be desirable to have a method for making an open cell alkenyl aromatic polymer foam wherein lower foaming temperatures may be employed.